Metallographic Failure Analysis on Bucket Elevator Conveyor Chain Links

Abstract

Failure analysis is a critical process aimed at determining the root cause of every failure. Failure of conveyor chain links in the industry has many repercussions which include; uncsheduled down - time which reduces production time coupled with damaged buckets and chain links which increases maintenance and repair cost. Failure of conveyor chain links and engineering structures on a whole is inevitable and for this reason, carrying out an investigation aimed at determining the root cause of failure is very crucial in that it can either minimize or prevent future reoccurances. Visual examination, chemical analysis and metallographic analysis were performed on both failed and un - failed conveyor chain link samples. Visual examination revealed that the type of failure was brittle fracture in that there was no necking. In addition, visual examination reavealed that there was an offset between the sprockets evidenced by indentations on the outer link of the chain link as well as vibrations within the bucket elevator system. Also, the point of fracture initiation was dependant on where the inclusions which were the cause of failure were located; either at the core or at the boundary surafce. Chemical analysis performed established that Silicon (Si), Phosphorus (P), Sulphur (S), Manganese (Mn), Chromium (Cr) and Molybdenum (Mo) all met the British standard EN 10293 requirement for steel casting for engineering use but Carbon (C) did not. Metallographic analysis carried out on the conveyor chain links showed that the cracks had initiated from dissolved micro - inclusions and were therefore the root cause of failure. It was therefore established that brittle fracture induced by inclusions was the root cause of failure of the conveyor chain links. In order to nullify the effect of the micro - inclusion, it was recommended that a stress concentration factor for inclusions should be introduced in the design of these conveyor chain links so as to improve on their fatigue life.